Ejectors, jet pumps and eductors have been used for many years in different applications as a means of pumping, vacuuming and mixing. The ejectors operate on the principle of a venturi, through which an energized fluid is directed causing a differential pressure across an orifice situated in a mixing chamber. The mixing chamber has a port to allow gases at a lower pressure than the energizing fluid pressure to be drawn into the chamber due to the created differential between the energized/pressurized line and the lower pressure inlet line. The mixed fluids depart from the chamber at a reduced pressure less than the inlet energized fluid but greater than the lower pressure fluid drawn into the mixing chamber.
Systems utilizing ejectors are not new in the art. U.S. Pat. Nos. 6,199,834 and 6,234,760 teach liquid gas ejectors, U.S. Pat. No. 7,326,285 teaches the use of an ejector for recovering hydrocarbon vapours and reuse of those vapours in alcohol manufacturing.
Ejectors were also used in vapour recovery systems. U.S. Pat. Nos. 6,418,957 and 6,315,000 and US Patent application US2002/0043289 teach eductor system and method of vapour recovery. These patents describe closed systems in which the collected gases are injected back into the recovery process by reducing emission and improving yields. This process is highly dependent on the pressures of the inlets and outlets which have an affect downstream of the process. Further, closed systems require additional equipment to deal with the safety of the system.
Unlike the vapour recovery in conventional oil extraction processes the operations in Steam Assisted Gravity Drainage (SAGD) oil recovery takes place under different conditions. These conditions include a source of high pressure gas for energized fluid and use for the mixed fluids outlet stream. Further SAGD operation has different contents of vapours than the conventional oil extraction.
Currently, in a SAGD facility there are atmospheric tanks containing hydrocarbons or residual hydrocarbons in water such as the dilbit, diluent, and produced water tanks. As these tanks are filled or heated up due to ambient conditions, there is a need to vent the vapours to prevent the tanks from over-pressuring. Since the tanks can contain toxic or flammable gases, discharging the gases to atmosphere on a normal basis is not acceptable. The low design pressure of the tanks prevents venting the vents to flare. These tanks require a system to collect and safely dispose of these gases. The industry standard solution for the recovery of low pressure gases is the use of a Vapour Recovery Unit (VRU). A typical VRU system consists of a compressor, aftercooler and discharge separation drum where the collected vapours are compressed and sent to the fuel gas system for disposal. These systems are expensive, vulnerable to malfunctions and require regular maintenance.
One objective of the present invention is to develop a vapour recovery system tailored for an SAGD process. This system should be inexpensive, easy to maintain and operate, and reliable. This system should also be compatible with a mobile modular SAGD process.
Further and other objects of the invention will become apparent to one skilled in the art when considering the following summary of the invention and the more detailed description of the preferred embodiments illustrated herein.